How is information encoded on the magnetic stripe?
A. Each character that is encoded on the stripe is made of a number of bits. The polarity of the magnetic particles in the stripe are changed to define each bit. Several schemes exist to determine whether each bit is a one or a zero, the most commonly used schemes are F2F (or Aiken BiPhase) and MFM (Modified Frequency Modulation). The ISO/IEC 7811 standards specify F2F encoding. In this encoding, each bit has the same physical length on the stripe. The presence or absence of a polarity change in the middle of the bit dictates whether it is a one or a zero. The width of a single bit always remains the same but some bits have an extra polarity change in the middle and these are called ones. MFM encoding is more complicated. This type of encoding allows twice as much data to be encoded with the same number of flux reversals (edges). For more details on MFM the reader is referred to AIM publication “Modified Frequency Modulation (MFM) for Magnetic Stripes”. The choice of encoding scheme is
